Pump



Dec. 8, 1964 T. BuDzlcH 3,160,110

PUMP

Filed Sept. 1l, 1962 2 Sheets-Sheet 1 1 N VENTOR.

746505Z aaZ/c/ Dec. 8, 1964 T. BuDzlcH 3,160,110

PUMP

Filed Sept. 11, 1962 2 Sheets-Sheet 2 INVEN TOR.

rac-MS2 a02/CH United States Patent O N' Minimi PURE? Tadeusz Budzicli, Shaker Heights, (Ehio, assigner to The Weatherhead Qompany, Cleveland, Ghia, a corporaftion of @hin Filed Sept. ll, i962, Ser. N 222,384 lll laims. (Si. 1103-173) This invention relates generally to pumps and more particularly to positive displacement pumps of the aXial piston type. This application is a continuation in part of the present inventors copending applications Ser. No. 825,005 tiled iuly 6,1959, now Patent No. 3,087,432 and Ser. No. 88,142 filed February 9, 1961, now Patent No. 3,090,312.

Atrial piston type pumps are commonly made with a non-rotatably cylinder block having a plurality of aXially aligned cylinder bores therein. The pistons extend into one end of the cylinder bores and are reciprocated by a rotary drive mechanism using a rotary cam to progressively reciprocate the pistons in a sequential manner so that some of the pistons are on their forward strokes while others are on their rearward or retraction strokes to obtain overlapping pumping strokes among the Various eylinders for purposes of smoothness and uniformity of the output tlow. It has been proposed to employ a rotary swash plate which bears directly against the pistons and rotates relative to the pistons, but this structure has the disadvantage that the sliding friction between the ends of the pistons and the swash plate creates a high amount of rubbing friction and a side thrust upon the pistons which tends to cock them and cause them to bind within their cylinders.

It has also been proposed to use a wobble plate which does not rotate but is progressively oscillaled by a rotating cam member in which the pistons are connected to the wobble plate by means of push rods to reduce the side thrust upon the pistons and so that the only rubbing friction occurs between the driving cam and the wobble plate where it may be easily minimized by proper thrust bearing design. In this arrangement, the push rods act as a rigid link under compression on the forward or pumping strokes of the pistons. In order to retract the pistons, the piston rods have been connected in ball and socket joints to both the piston and the wobble plate so that they are placed in tension to retract the piston. This tension creates a tendency for the wobble plate to cock by pulling it away from Contact with the driving cani and also requires a relatively complicated ball and socket joint at both the piston and wobble plate ends of the push rod.

It has been recognized that it is desirable to avoid the problem of this latter construction by employing springs to retract the pistons, since this arrangement insures that the push rod will always be in compression to maintain a thrust against the wobble plate. However, such constructions have heretofore been limited to pumps or" relatively short stroke in which the angularity ot motion between the wobble plate and the piston is at a minimum in order to avoid displacement of the push rod from either of its sockets in case the piston should stick in the forward position. If this should happen, the push rod will tend to cock on the reaction stroke since it is pulled free from its engagement with either the piston or the wobble plate and unless the angularity of the wobble plate and the length of stroke are quite small, the amount of misa1ignment will be so great as to allow the push rod to engage either the piston or t e wobble plate at some point other than the proper socket recess with consequent damage to the pump.

It is therefore a primary object of this invention to provide a drivefor reciprocating the pistons in an axial piston lbl l0 Patented Een. 8, 1964 pump in which the piston, the push rod and the wobble plate are constructed to insure that the push rod will be self-aligning and will always return to its proper seat in the piston and wobble plate in the event of the piston sticling at the forward position.

Another object of this invention is to provide an axial piston pump as set forth in the preceding object which allows a high degree of angularity in the motion of the wobble plate to provide a relatively long stroke with a short push rod to maintain a compact size for the pump.

lt is another object of this invention to provide an axial piston pump as set forth in the preceding objects in which the reciprocating parts have minimum inertia to allow operation at high speed with relatively low stresses.

lt is another object of this invention to provide a drive structure for reciprocating the pistons in an axial piston purnp as set forth in the preceding objects which minimizes the cooking and side thrust on the pistons and wobble plate.

Still another object of this invention is to provide in an axial piston pump according to the preceding objects a piston, push rod and wobble plate arrangement which is simple in construction to allow low cost manufacture, while retaining a high degree of strength and rigidity to minimize the weight of the various parts.

Further objects and advantages of this invention will readily become apparent to those skilled in the art upon a more complete understanding of the invention, the preerred embodiment of which is shown in the drawings and described in the following detailed description.

ln the drawings:

1 is a longitudinal cross-sectional view of a pump incorporating the present invention;

FlGURE 2 is an enlarged fragmentary cross-sectional view of a piston, push rod and wobble plate with the wobble plate in the rearward position and the piston in the forward position with the push rod out of engagement with the wobble plate;

FIGURE. 3 is a fragmentary view similar to FlGURE 2, but showing the push rod out of engagement with the piston; and i FGURE 4 is a view of a modified form of push rod for use in the pump shown in FIGURES 1 through 3.

Referring now to the pump shown in FIGURE l, the pumping mechanism is incorporated within a pump housing l0 which dehnes a fluid chamber 11 therein. The chamber l1 is lled with fluid through an inlet 12 which is connected to a suitable huid supply as a reservoir. The pump housing l@ may be provided with a radial flange 13 having bolt holes 14 therethrough for mounting of the pump.

At one end, the pump housing it? is closed ot by an end cap le secured to the housing (l0 by suitable cap screws 17. The pump outlet 1S is shown as centrally located on end cap 16 for connection tothe rest of the tluid power System. An end plate 2li is mounted within the pump housing l0 and held in place by the end cap 16. A suitable -O-ring seal 2l may be provided to prevent leakage between the pump housing lil and end plate 2li. The end cap i6 and end plate 2t) may be secured together to prevent rotation by a suitable dowel pin 22.

The end plate Ztl has a tubular guide 23 integral therewith and projecting axially into the iiuid chamber 11 along the longitudinal axis of the pump. A cylinder block 25 is slidabiy mounted on the tubular guide 23 for axial reciprocating motion and is prevented from rotating on the tubular guide 23 by means of a pin 26 carried by the cylinder block and engaging a longitudinal groove 27 on the outer periphery of tubular guide 23. The cylinder block 25 has a plurality of axial cylinder bores Sli extending therethrough and arranged equidistantly around the longitudinal axis. Since all of the cylinder bores and their associated piston structurey are identical, only oney cylinder bore has been shown in the drawings and will be described hereinafter.

A pumping piston 32 fits into the end of cylinder bore 30 away from the end plate 20 and is reciprocated by the mechanism to be described in greater detail hereinafter. The cylinder blocle25 has an outer peripheral slot 33 which opens into the cylinder bore 30 t'o provide an inlet port 34. It will be appreciated that longitudinal movement of the cylinder block 25 positions theport 34 with respect to the stroke of the piston 32 to vary the output displacement of the pump by varying the point along the piston stroke at which the inlet port is sealed oftr to allow the remaining iiuid in the cylinder bore to be pumped to the pump outlet 18.

A tubular reaction piston 36 fits into the end of cylinder bore 30 opposite the pumping piston 32 and is provided with a bore 37 therethrough to conduct iluid from the cylinder bore. The end cap 16 has a chamber 39 formed therein in alignment with the reaction piston 36 and a tubular port member 40 having a bore 41 therethrough is positioned within chamber 39 and projects through an opening 43 in the end plate 20 to make face-to-face sealing vcontact with the adjacent end of the reaction piston 36. In order to maintain the reaction piston 36 in sealing engagement with the port member 40, a helical compression spring 45 is tted around the reaction piston 36 to bear the one end against the cylinder block 25 and at the other end against an abutment 46 carried on the end of the reaction piston 36 adjacent port member 40. The bore 41 and port member 40 is closed off within chamber 39 by a check valve plate 48 which is held in place by the biasing force of a check valve spring 49. A passage 50 conducts the fluid pumped past the check valve into chamber 39 to the pump outlet 1S.

The pump is provided with a pressure compensated control valve adapted to shift the axial position of the cylinder block 25 to reduce the output displacement of the pump when the output pressure exceeds a predetermined level t'o prevent excessive pressure in the pump outlet 18. This pressure compensated valve is described in detail in the present inventors copending applications Serial No. 825,005, tiled July 6, 1959 and Serial No. 847,512, tiled October 20, 1959, now Patent No. 3,117,524.

Brieily, the pressure compensated valve includes a valve spool 52 slidably mounted within a bore 53 formed in the end plate 20 and tubular guide'23. Valve spool 52 has a centralvland portion 55 formed by outer and innerk annular grooves S6 and 57. The outer annular groove 56 is connected through passage 58 to the pump outlet 18 so that it is exposed to full outlet pressure at all times. The inner groove 57 is connected through a drain passage 59 to the fluid chamber 11 within the pump housing. A radial port 60 is in axial alignment with the land 55 and connects through a passage 61 to a chamber 62`within the inner end portion of the tubular guide 23. Thus, depending upon the position of the land 55, the chamber 62 will either be closed oil? when land 55 closes off the port 60, or it will be connected to either pump outlet pressure or to drain When the port 60 is connected to the outer groove 56 or the inner groove 57, respectively. The chamber 62 is in turn connected through a radial passage 64 and annular axial passage 65 to a motor chamber 66 formed within the cylinder block 25 and closed oi at its outer end by a piston 68 xedly secured to the end of tubular guide 23.

When uid pressure is admitted in the motor chamber 66, it exerts a biasing force upon the cylinder block 25 to shift the latter toward the end plate 20 against theV biasing force of the compression springs 45 surrounding the reaction pistons 36. The shifting of theV cylinder block in this direction, which is accomplished whenever the pump outlet pressure exceeds the predetermined level,

moves the .inlet ports 34V toward the end of the piston stroke to reduce the effective output volume of the pump.

v Likewise, when the chamber 62 is connected to drain, fluid of the pump.

The position of the valve spool 52 is controlled by the balance between the force of the pump outlet pressure acting upon the exposed end 69 of the valve spool within the pump outlet 18 and the force of the control spring '70 which is mounted within the chamber 62 to abut one end against the valve spool 52 and at the other end against an abutment plug 71 carried in the outer end of chamber 62. Thus, the preload and stitness of the control spring 70 determines the magnitude of the outlet pressure acting on end 69 necessary Ito shift the valve spool 52 in a direction to have the outer groove 56 in alignment with the port 60' to allow the fluid pressure at the outlet to ow into the motor chamber 66 to reduce the effective output volume of the pump.

Turning now to the remainder of the pump structure, a plate 73 has a shank portion 74 tted within the end of tubular'guide 23 outward of the abutment plug 71.

late '73 extends radially outward on the side of the cylinder block 25 away from the end plate 20 and is suitably apertured at 75 to allow the pistons 32 to extend therethrough.

The drive for reciprocating the ypistons 32 is mounted within the pump housing 10 at the end opposite that containing the cylinder block 25. At the end opposite the end cap 16, pump housing 10 is provided with an end wall 77' having an aperture 78 therein to receive a drive shaft 80. The drive shaft 80 has the outer end 81 formed to mount a belt sheave or gear for driving connection to a prime mover. At its inner end, drive shaft 80 has a reduced pilot portion 83 which is journaled within the shank portion 74 of plate 73 to provide a rigid bearing mount for the drive structure.V A drive member 85 is tted on drive shaft 80 and rotatably driven therewith by the spline connection at 86. The drive member 85 is journaled by a bearing 88 Xedly secured in the end wall 77 by a dowell pin 89. The bearing member 88 serves as both a radial and thrust bearing for the drive member 85. The drive member 85 also supports an inclined bearing member 92 which is pinned to the drive member by a suitable dowel pin 93 and'rotatably journals the wobble plate 95 which has a shank portion 96 extending within the bearing member 92. The bearing structure for the drive member 85 and wobble plate 95 is disclosed in greater detail in the present inventors copending application Serial No. 17,832, filed March 28,- 1960.

The wobble plate 95 is progressively tilted or oscillated by the inclined bearing member 92 and is prevented from rotating with the drive member 85 by Ithe projecting stud 98 which rotatably supports a bearing block 99 adapted to slide axially within the Walls 102 of a guide channel 101. Since the guide channel 101 restrains the motion of bearing block 99 to motion in a plane passing through the drive axis, the oscillation of wobble plate 95 imparts a generally sinusoidal reciprocating motion to any given point on its face.

The wobble plate 95 is provided on the face away from the bearing member 92 with a cup-like recess 104 in axial alignment with they piston 32. The recess 104 receives one ball end 105 of a rigid push rod 106, the other end of which is provided with another ball end 108 which engages a hemispherical recess 110 on theV 'underside of the head 109 of piston 32. The piston 32 against a spring abutment 115 carried on the end of the tubular skirt 112.

Intermediate the ball ends 165 and 108, push rod 1% is provided with an enlarged portion 118 which, as shown in FIGURE l, is in axial alignment within a large counterbore portion 121 of the tubular piston skirt 112. The piston 32 has a smaller bore 12? extending from the inner end of the counterbore 121 toward the head 199 adjacent the recess 11i) receiving the ball end S.

It will be seen that when the recess 104 on wobble plate 95 is moved in the forward or pumping stroke direction toward the plate 73, the rigid push rod 1% moves the piston 32 on the forward or pumping stroke. As the recess 194 moves backwards on the return stroke, the return spring 114 forces the piston 32 and push rod 1196 rearwardly so that normally both ball ends 105 and 16S of push rod 1116 remain firmly seated within their respective recesses. However, it is possible that because of dirt or damage the piston 32 may stick in the forward position at the end of the pumping' stroke and the biasing force of the return spring 11d may not be sui'licient to move the piston rearwardly on its return stroke with the wobble plate. In this situation, as shown in FIGURE 2, the push rod 1% because of its inertia will usually remain with the piston 32 in the forward position so that the ball end 168 is retained in contact with the recess 11i) of the piston head 1139. AS a result, the other ball end 1115 is disengaged from the cup-like recess 104, and since this end of the piston rod is then unsupported, it will fall under the action of gravity until the enlargement 113 rests in contact with the wall of the counterbore 121. However, when the wobble plate again moves on its forward stroke, the conical walls 123 of recess 134, which at all times extend radially outwardly of the ball end 195, guide the ball end so that it is automatically reseated in recess 164 at the forward end of the stroke of the wobble plate 95. Thus, even though the push rod 1% may move slightly out of alignment because of the disengagement of the ball end 1495 from the recess 1h14, it will automatically be moved back into alignment on the forward stroke by virtue of the engagement of the ball end 105 with the conical walls 123 of the recess 10d.

It may also happen that when the piston 32 remains stuck in the forward position, the piston rod may remain in engagement with the recess 104 so that the other ball end 108 moves away from the recess 11i) on the piston head. In this case, the push rod 1% will assume the position shown in FIGURE 3 in which the enlargement 11S moves downward to make sliding Contact to the counterbore 121 while the ball end 168 contacts the inner surface of the smaller bore 120. Thus the amount of angular misalignment of the push rod 106 is t limited and on the forward stroke, the ball end 1% will reseat in the hemispherical recess 110. Thus, the restraining action of counterbore 121, bore 120 and enlargement 118 together with the corneal walls 123 of recess 10d serve to limit the amountuof angular misalignment of the push rod 105 as shown in FIGURES 2 and 3 and prevent any possible damage as a result of misalignment in the case of piston 32 sticking in the forward position.

Since the sticking of the piston 32 is therefore not likely to permanently damage the pump and may free itself during continued operation of the pump, the return spring 114 can be made relatively light in force to minimize the force on the wobble plate 95 and thereby reduce the total amount of `thrust absorbed by the bearings 92 and SS. Furthermore, the shape of the wobble plate 95, push rod 106, and piston 32 is such that they are easily machined to the desired shape and since the ball and socket joints formed by the ball pins 135 and 10S in the recesses 164 and 110 need to absorb thrust loads only, the use of additional parts to enclose the ball por- 6 tions and 108 over more than the hemisphere are unnecessary since these portions would only be required if the push rod 166 were placed in tension on the return stroke, an arrangement which is made unnecessary by the use of the return spring 114. Furthermore, the push rod and piston are quite light in weight to minimize the inertial forces and reduce the driving loads at high pump speeds.

An alternative construction for the push rod is shown in FIGURE 4, it being understood that the push rod of FGURE 4' may be substituted for the push rod 1%l in the pump shown in FIGURES l through 3. The push rod 13@ is made of a uniform diameter rod throughout its mid-section and is enlarged to form at one end a ball portion 131 for engagement with the recess 104 and wobble plate 95. The other end of push rod is likewise formed with an enlarged ball portion 133 for engagement with the hemispherical recess 11i) on the piston head 169. lowever, the enlargement on ythe mid-portion of push rod 139, instead of being formed as a solid integral portion of the push rod, as is enlargement 11S on push rod 1%, is formed by adding a separate washer which slips over the push rod 13@ and is held in place by welds indicated at 136, rhe washer may be split so that it may be inserted radially around the push rod 13), or it ay be placed on the rod 13d before the ball ends 131 and 133 are formed. It will be appreciated that push rod 1116 with its integral enlargement 118 may be formed by machining a solid bar having a diameter at least as great as enlargement 118. The push rod 130 may be formed from a length of rod having the same diameter as the body of lthe push rod, and the ends may be headed or upset for forming the ball portions 131 and 133. In the latter case, the washer 135 may simply be slipped in place before the upsetting of the ball ends and therefore need not be split and may have an inner diameter substantially the same as that of the push rod. It will be appreciated that the washer 135 functions in the same manner as enlargement 118 in engaging the counterbore 121 of piston 32 in the manner set forth hereinabove and shown in detail in FIGURES 2 and 3.

While the present invention has been shown .and described in considerable detail, it is recognized that various modifications and rearrangements will readily become apparent to those skilled in the art upon a more complete understanding of the invention, and such modifications and rearrangements may be resorted to without departing from the scope of the invention asset forth in the following claims.

What is claimed is:

l. A pump comprising a pump housing, a cylinder block mounted in said pump housing, said cylinder block havin-g `at least one cylinder bore therein, a piston reciprocable in said cylinder bore, wobble plate in said pump housing, a rotatable drive cam having an inclined face adapted to oscillate said wobble plate, means to prevent said wobble -plate from rotating with respect to said cylinder block, spring means biasing said piston toward said wobble plate, a push rod having opposed ends engageable with said wobble plate and said piston to shift said piston -against said spring means, said piston having a head portion spaced axially from said wobble plate, a push rod seat on said head portion facing said wobble plate, a push rod eat on said wobble plate facing said piston, said piston having a tubular skirt portion extending from said head portion toward said wobble plate, said push rod extending Ifor more than half its length within said skirt portion with one end engageable with said head portion seat and the other end engagea-ble with said wobble plateseat, said -push rod having an enlarged portion intermediate the ends axially within said skirt portion and engageable with the interior wall thereof when one of said push rods is disengaged from its l`adjacent seat to limit the amount of tilting misalignme-nt of said push rod, said `push rod having reduced diameterportions on each side of said enl-arged portion extending from said enlarged portion to the push rod ends.

2. A pump comprising a pump housing, a cylinder block mounted in -said pump housing, said cylinder block having at least one cylinder bore therein, a piston reciprocable in said cylinder bore, a wobble plate in said pump housing, a rotatable drive cam having an inclined tace adapted to oscillate said wobble plate, means to prevent said wobble plate from rotating with respect to said cylinder block, spring means biasing said piston toward said wobble plate, a ypush rod having opposed ends engageab-le with said wobble plate and said piston to shi-ft said piston vagainst said spring means, said piston having a head portion spaced axially yfrom said wobble plate, a recess on .said head Iportion facing said wobble plate, a recess on said wobble lplate yfacing said piston, said piston having a tubular skirt portion extending from said head portion toward said wobble plate, said push rod extending for more than half its length within said skirt portion with onel end engageab'le with said head portion recess and the other end engageable with said wobble plate recess, said push rod having an enlarged portion intermediate the ends axially within said skirt portion and engageable wit-h the interior Wall thereof when one of said push rod ends is disengaged from its` adjacent recess to limit the amount of tilting misalignrnent of said push rod with respect to said piston yand wobble plate recesses, said push rod having reduced diameter portions on each side of said enlarged portion extending from said enlarged portion to the push rod ends.

3. A pump comprising a pump housing, a cylinder block mounted in said pump housing, said cylinder block having lat least one cylinder bore therein, a piston reciprocable in said cylinder bore, ya wobble plate in said pump housing, a rotatable drive cam having an inclined face adapted to 'oscillate said wobble plate, means to prevent said wobble plate from rotating with respect to said cylinder block, spring means biasing said piston towards said wobble plate, a push rodhaving opposed ends engage/able with said wobble plate and said piston to shift said piston against said spring means, said piston having a head portion spaced axially from said wobble plate, a recess on said head portion yfacing said wobble plate, a recess on said wobble plate facing said piston, said piston having a tubular skirt :portion extending from said head portion toward said wobble plate, said push rod extending for more than half its length within said skirt portion with one end engagea'ble lwith said head portion recess and the other end engageable with said wobble plate recess, said push rod having an enlarged portion intermediate the endsyaxially within said skirt portion and engageable with the interior wall thereof when one of said push rod ends is disengaged from its adjacent recess to limit the `amount of ltilting misalignment of said push rod with respect to said pist-on and wobble plate recesses, said push rod having reduced :diameter portions on each side of said enlarged portion extending from said enlarged portion to the push rod ends, said wobble plate recess having outwardly flaring sides, the outer end of said wobble plate recess dehning [an opening havin-g a diameter greater than the maximum amount of tilting misalignment oi the adjacent push rod end. v

4. A pump comprising `a pump housing, a cylinder block mounted in said pump housing, said cylinder block v having at least one cylinder bore therein, a piston reciprocable in said cylinder bore, a wobble plate in said pump housing, a rotatable drive cam having an inclined tace adapted to oscillate said wobble plate, means to prevent said wobble plate from rotating with respect to said cylinder block, spring means biasing said piston toward said wobble plate, -a push rod engagea-ble with said wobble plate -and said piston to shift said piston against said spring means, said piston having a head portion spaced axially from said wobble plate, a hemispherical recess on said head portion facing said wobble plate, a hemispherical recess on said wobble plate yfacing said piston,

said piston having a tubular skirt portion extending from said head portion toward said wobble plate, said push rod extending `foi more than half its length within said skirt portion, said push rod having one spherical end engagefable with said head portion recess, said push rod having a second spherical end engageable with said wobble plate recess, said push rod having an enlarged portion intermediate said spherical ends .axially ywithin said skirt portion, said push rod havingreduced diameter portions on each side of said enlarged portion 'extending from said enlarged portion to said spherical ends, said enlarged portion having a diameter greater than that of said spherical push rod ends land engageable with the interior wall of said tubular skirt when one of said push rod ends is disengaged trom the ,adjacent recess to limit the amount of tilting misalignment of said push rod with respect to said piston and wobble plate recesses.

5. A pump comprising a pump housing, a cylinder block mounted in said pump housing, said cylinder block having atleast one cylinder bore therein, a piston reciprooable in said cylinder bore, a wobble plate in said pump housing, a rotatable drive cam having an inclined lace adapted to foscillate said wobble plate, means to prevent said wobble plate yfrom rotating with respect to said cylinder block, spring means biasing said piston towards said wobble plate, a push rod engageable with said wobble plate and said piston to shift said piston against said spring means, said piston having a. head portion spaced axially `from said wobble plate, a recess on said head portion facing said wobble plate, a recess on said wobble plate facing said piston, said piston having a tubular skirt portion extending `from said head 'portion toward said wobble plate, said tubular skirt portion having a counterbore extending from .the end adjacent said wobble plate to a point a spaced distance from said head portion recess, said skirt portion having a reduced bore extending from the inner end of said counterbore-'to said head portion recess, said push rod being positioned ttor more than half its length wit-hin said reduced bore 'and said counterbore of said skirt portion with one end eng-ageable with said head portion recessand the other end engageable with said wobble plate recess, said push rod having an enlarged portion intermediate the ends [axially within said counterbore of said skirt portion and engageable with interior wall thereof when one of said push rod ends is disengaged lfrom its adjacent 4recess to limit the amount of tilting mis- :alignment of said push rod with respect to said piston and wobble plate recesses, said push rod having reduced diameter portions on each side of said enlarged porti-on extending from said enlarged portion to the push rod ends.

6. A pumpas set forth in claim l wherein said enlarged portion on said push rod is lformed integrally with said push rod and said push rod ends.

7. A pump as set ltort-hin claim l wherein said enlarged portion 'on said push rod is'a separate washershaped member iixe/dly secured to said push rod intermediate the ends.

8. A reciprocating hydraulic piston mechanism comprising a body having a cylinder bore therein, a piston reciprocable in said cylinder bore, a reciprocable member cyclically movable in timed relationship with said piston, spring means biasing said pist-on towards said reciprocable member, said piston having a `head portion within said cylinder bore, a push rod seat on said head portion facing saidV reciprocable member, la push rod seat on said reciprocable member 4facing said piston, said piston having a tubular skirt portion extending from said head portion toward said reciprocable member, a push rod extending for more than half its length within said skirtportion with one end engageable with said head portion seat and the other end engageable with said reciprocable member seat, said `push rod having an enlarged portion intermediate the ends axially within said skirt portion and engageable with the interior wall thereof when one of said push rod ends is disengaged from its adjacent seat to limit the amount of tilting misalignment of said push rod with respect to said seats, said push rod having reduced diameteportions on each side of said enlarged portion extending from said enlarged portion to the push r-od ends.

9. A reciprocating hydraulic piston mechanism cornprising a .body having a cylinder bore therein, a piston reciprocable in said cylinder bore, a reciprocable member cyclically movable in timed relationship with said piston, spring means biasing said piston toward said reciprocable member, said piston having a head portion within said cylinder bore, a hemispherical recess on said head portion facing said reciprocable member, a hemispherical recess on said reciprooable member facing said piston, said piston having a tubular skirt portion extending from said head portion toward said reciprocable member, a push rod extending 'for mroe than half its length Within said skirt portion, said push rod having one spherical end engageable With said head portion recess, said push rod having a second spherical end engagealble with said reciprocable member recess, said push rod having an enlarged portion intermediate said spherical ends axiaily within said skirt portion, said enlarged @portion having a diameter greater than that of said spherical push rod ends and engageabie with the interior Wall of said tubular skirt when one of said push rod ends is disengaged from the adjacent recess to limit the amount of tilting misalignment of said push rod `with respect to said piston and reciprocable member recesses, said push rod having reduced diameter portions on each side of said enlarged portion extending from lsaid enlanged portion to said spherical ends.

l0. A reciprocating hydraulic piston mechanism cornprising a body having a cylinder bore therein, a piston reciprocable in said cylinder bore, `a reciprocable member cyclically movable in timed relationship with said piston,

spring means biasing said piston towards said reciprocable member, said piston having a head portion within said cylinder bore, a hemispherical recess on said head portion yfacing said reciprocable member, a hemispherical recess on said reciprocable member having conical sides daring outwardly toward said piston, said piston having a tubular skirt portion extending from said head portion toward said reciprocable member, said tubular skirt portion having a counterbore extending from the outer end to a point a spaced distance from said head portion recess, said skirt portion having a reduced bore extending lfrom the inner end of said counterbore to said head portion recess, a push rod extending for more than half its length within said reduced bore and said counterbore of said skirt portion Aand having one end engageable with said head portion recess and the other end engageable with sai-d reciprocab'le member recess, said push rod having an enlarged portion intermediate the ends axiaily Within said counterbore lof said skirt portion and engageable with interior wall thereof when one of said push rod ends is disengaged from its adjacent recess to limit the amount of tilting misalignment of said push 4rod with respect to said recesses, said push rod having reduced diameter portions on eaoh side of said enlarged portion extending from said enlarged portion to the push rod ends.

References Cited bythe Examiner UNITED STATES PATENTS 2,237,518 4/41, Blum 74-60 2,361,046 10/44 Molly 103-162 2,860,517 11/58 C-auble 103--173 FOREIGN PATENTS 1,065,875 1/54 France.

764,143 5 S2 Germany.

LAURENCE V. EFNER, Primary Examiner. 

1. A PUMP COMPRISING A PUMP HOUSING, A CYLINDER BLOCK MOUNTED IN SAID PUMP HOUSING, SAID CYLINDER BLOCK HAVING AT LEAST ONE CYLINDER BORE THERIN, A PISTON RECIPROCABLE IN SAID CYLINDER BORE, WOBBLE PLATE IN SAID PUMP HOUSING, A ROTATABLE DRIVE CAM HAVING AN INCLINED FACE ADAPTED TO OSCILLATE SAID WOBBLE PLATE, MEANS TO PREVENT SAID WOBBLE PLATE FROM ROTATING WITH RESPECT TO SAID CYLINDER BLOCK, SPRING MEANS BIASING SAID PISTON TOWARD SAID WOBBLE PLATE, A PUSH ROD HAVING OPPOSED ENDS ENGAGEABLE WITH SAID WOBBLE PLATE AND SAID PISTON TO SHIFT SAID PISTON AGAINST SAID SPRING MEANS, SAID PISTON HAVING A HEAD PORTION SPACED AXIALLY FROM SAID WOBBLE PLATE, A PUSH ROD SEAT ON SAID HEAD PORTION FACING SAID WOBBLE PLATE, A PUSH ROD SEAT ON SAID WOBBLE PLATE FACING SAID PISTON, SAID PISTON HAVING A TUBULAR SKIRT PORTION EXTENDING FROM SAID HEAD PORTION TOWARD SAID WOBBLE PLATE, SAID PUSH ROD EXTENDING FOR MORE THAN HALF ITS LENGTH WITHIN SAID SKIRT PORTION WITH ONE END ENGAGEABLE WITH SAID HEAD PORTION SEAT AND THE OTHER END ENGAGEABLE WITH SAID HEAD PORTION SEAT AND SAID PUSH ROD HAVING AN ENLARGED PORTION INTERMEDIATE THE ENDS AXIALLY WITHIN SAID SKIRT PORTION AND ENGAGEABLE WITH THE INTERIOR WALL THEREOF WHEN ONE OF SAID PUSH RODS IS DISENGAGED FROM ITS ADJACENT SEAT TO LIMIT THE AMOUNT OF TILTING MISALIGNMENT OF SAID PUSH ROD, SAID PUSH ROD HAVING REDUCED DIAMETER PORTIONS ON EACH SIDE OF SAID ENLARGED PORTION EXTENDING FROM SAID ENLARGED PORTION TO THE PUSH ROD ENDS. 